CustomAlert refactoring. Using proper UIPresentationController with adaptive margins

main/Common Classes/SlideInAnimation.swift

@@ -0,0 +1,190 @@
+import UIKit
+
+enum PresentationEdge { case left, top, right, bottom }
+
+// ########################################
+// #
+// #    MARK: - Transitioning Delegate
+// #
+// ########################################
+
+class SlideInTransitioningDelegate: NSObject, UIViewControllerTransitioningDelegate {
+	private var edge: PresentationEdge
+	private var modal: Bool
+	private var dismissable: Bool
+	private var shadow: UIColor?
+	
+	init(for edge: PresentationEdge, modal: Bool, tapAnywhereToDismiss: Bool = false, modalBackgroundColor color: UIColor? = nil) {
+		self.edge = edge
+		self.dismissable = tapAnywhereToDismiss
+		self.shadow = color
+		self.modal = modal
+	}
+	
+	func presentationController(forPresented presented: UIViewController, presenting: UIViewController?, source: UIViewController) -> UIPresentationController? {
+		StickyPresentationController(presented: presented, presenting: presenting, stickTo: edge, modal: modal, tapAnywhereToDismiss: dismissable, modalBackgroundColor: shadow)
+	}
+	
+	func animationController(forPresented _: UIViewController, presenting: UIViewController, source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
+		SlideInAnimationController(from: edge, isPresentation: true)
+	}
+
+	func animationController(forDismissed _: UIViewController) -> UIViewControllerAnimatedTransitioning? {
+		SlideInAnimationController(from: edge, isPresentation: false)
+	}
+}
+
+// ########################################
+// #
+// #    MARK: - Animated Transitioning
+// #
+// ########################################
+
+private final class SlideInAnimationController: NSObject, UIViewControllerAnimatedTransitioning {
+	let edge: PresentationEdge
+	let appear: Bool
+	
+	init(from edge: PresentationEdge, isPresentation: Bool) {
+		self.edge = edge
+		self.appear = isPresentation
+		super.init()
+	}
+	
+	func transitionDuration(using context: UIViewControllerContextTransitioning?) -> TimeInterval {
+		(context?.isAnimated ?? true) ? 0.3 : 0.0
+	}
+	
+	func animateTransition(using context: UIViewControllerContextTransitioning) {
+		guard let vc = context.viewController(forKey: appear ? .to : .from) else { return }
+		
+		var to = context.finalFrame(for: vc)
+		var from = to
+		switch edge {
+		case .left:   from.origin.x = -to.width
+		case .right:  from.origin.x = context.containerView.frame.width
+		case .top:    from.origin.y = -to.height
+		case .bottom: from.origin.y = context.containerView.frame.height
+		}
+		
+		if appear { context.containerView.addSubview(vc.view) }
+		else { swap(&from, &to) }
+		
+		vc.view.frame = from
+		UIView.animate(withDuration: transitionDuration(using: context), animations: {
+			vc.view.frame = to
+		}, completion: { finished in
+			if !self.appear { vc.view.removeFromSuperview() }
+			context.completeTransition(finished)
+		})
+	}
+}
+
+// #########################################
+// #
+// #    MARK: - Presentation Controller
+// #
+// #########################################
+
+private class StickyPresentationController: UIPresentationController {
+	private let stickTo: PresentationEdge
+	private let isModal: Bool
+	
+	private let bg = UIView()
+	private var availableSize: CGSize = .zero // save original size when resizing the container
+	
+	override var shouldPresentInFullscreen: Bool { false }
+	override var frameOfPresentedViewInContainerView: CGRect { fittedContentFrame() }
+	
+	required init(presented: UIViewController, presenting: UIViewController?, stickTo edge: PresentationEdge, modal: Bool = true, tapAnywhereToDismiss: Bool = false, modalBackgroundColor bgColor: UIColor? = nil) {
+		self.stickTo = edge
+		self.isModal = modal
+		super.init(presentedViewController: presented, presenting: presenting)
+		bg.backgroundColor = bgColor ?? .init(white: 0, alpha: 0.5)
+		if modal, tapAnywhereToDismiss {
+			bg.addGestureRecognizer(
+				UITapGestureRecognizer(target: self, action: #selector(didTapBackground))
+			)
+		}
+	}
+	
+	// MARK: Present
+	
+	override func presentationTransitionWillBegin() {
+		availableSize = containerView!.frame.size
+		
+		guard isModal else { return }
+		containerView!.insertSubview(bg, at: 0)
+		bg.alpha = 0.0
+		if presentedViewController.transitionCoordinator?.animate(alongsideTransition: { _ in
+			self.bg.alpha = 1.0
+		}) != true { bg.alpha = 1.0 }
+	}
+	
+	@objc func didTapBackground(_ sender: UITapGestureRecognizer) {
+		presentingViewController.dismiss(animated: true)
+	}
+	
+	// MARK: Dismiss
+	
+	override func dismissalTransitionWillBegin() {
+		if presentedViewController.transitionCoordinator?.animate(alongsideTransition: { _ in
+			self.bg.alpha = 0.0
+		}) != true { bg.alpha = 0.0 }
+	}
+	
+	override func dismissalTransitionDidEnd(_ completed: Bool) {
+		if completed { bg.removeFromSuperview() }
+	}
+	
+	// MARK: Update
+	
+	override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
+		availableSize = size
+		super.viewWillTransition(to: size, with: coordinator)
+	}
+	
+	override func containerViewDidLayoutSubviews() {
+		super.containerViewDidLayoutSubviews()
+		bg.frame = containerView!.bounds
+		if isModal {
+			presentedView!.frame = fittedContentFrame()
+		} else {
+			containerView!.frame = fittedContentFrame()
+			presentedView!.frame = containerView!.bounds
+		}
+	}
+	
+	/// Calculate `fittedContentSize()` then offset frame to sticky edge respecting *available* container size .
+	func fittedContentFrame() -> CGRect {
+		var frame = CGRect(origin: .zero, size: fittedContentSize())
+		switch stickTo {
+		case .right:  frame.origin.x = availableSize.width - frame.width
+		case .bottom: frame.origin.y = availableSize.height - frame.height
+		default: break
+		}
+		return frame
+	}
+	
+	/// Calculate best fitting size for available container size and presentation sticky edge.
+	func fittedContentSize() -> CGSize {
+		guard let target = presentedView else { return availableSize }
+		let full = availableSize
+		let preferred = presentedViewController.preferredContentSize
+		switch stickTo {
+		case .left, .right:
+			let fitted = target.systemLayoutSizeFitting(
+				CGSize(width: preferred.width, height: full.height),
+				withHorizontalFittingPriority: .fittingSizeLevel,
+				verticalFittingPriority: .required
+			)
+			return CGSize(width: min(fitted.width, full.width), height: full.height)
+		case .top, .bottom:
+			let fitted = target.systemLayoutSizeFitting(
+				CGSize(width: full.width, height: preferred.height),
+				withHorizontalFittingPriority: .required,
+				verticalFittingPriority: .fittingSizeLevel
+			)
+			return CGSize(width: full.width, height: min(fitted.height, full.height))
+		}
+	}
+}